You'd be better off building a "custom" passive network than just using one from another set. Doing might be cheaper than going with an active setup, but it's hard to tell. You might hit on a good freq that works right off the bat. You also might have to switch out components a bunch of times and still not get it sounding right. Going with an active setup using a continuously variable crossover with independant controls for high/low left and right freqs is the surest way to get it just right. This assumes that you take the time to tune it up.